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<!DOCTYPE document [
  <!ENTITY project SYSTEM "project.xml">
]>
<document url="cluster-interceptor.html">

  &project;

  <properties>
    <title>The Channel Interceptor object</title>
  </properties>

<body>

<section name="Table of Contents">
<toc/>
</section>

<section name="Introduction">
  <p>
  Apache Tribes supports an interceptor architecture to intercept both messages and membership notifications.
  This architecture allows decoupling of logic and opens the way for some very useful feature add-ons.
  </p>
</section>

<section name="Available Interceptors">
   <ul>
    <li><code>org.apache.catalina.tribes.group.interceptors.TcpFailureDetector</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.ThroughputInterceptor</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.MessageDispatchInterceptor</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.NonBlockingCoordinator</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.OrderInterceptor</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.SimpleCoordinator</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.TwoPhaseCommitInterceptor</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.DomainFilterInterceptor</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.FragmentationInterceptor</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.GzipInterceptor</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.TcpPingInterceptor</code></li>
    <li><code>org.apache.catalina.tribes.group.interceptors.EncryptInterceptor</code></li>
   </ul>
</section>

<section name="Static Membership">
  <p>
   In addition to dynamic discovery, Apache Tribes also supports static membership, with membership verification.
   To achieve this add the <code>org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor</code>
   after the <code>org.apache.catalina.tribes.group.interceptors.TcpFailureDetector</code> interceptor.
   Inside the <code>StaticMembershipInterceptor</code> you can add the static members you wish to have.
   The <code>TcpFailureDetector</code> will do a health check on the static members,and also monitor them for crashes
   so they will have the same level of notification mechanism as the members that are automatically discovered.</p>
   <source><![CDATA[     <Interceptor className="org.apache.catalina.tribes.group.interceptors.StaticMembershipInterceptor">
       <LocalMember className="org.apache.catalina.tribes.membership.StaticMember"
                  domain="staging-cluster"
                  uniqueId="{1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,1}"/>
       <Member className="org.apache.catalina.tribes.membership.StaticMember"
                  port="5678"
                  securePort="-1"
                  host="tomcat01.mydomain.com"
                  domain="staging-cluster"
                  uniqueId="{0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}"/>
     </Interceptor>]]></source>
</section>

<section name="Attributes">

  <subsection name="Common Attributes">
   <attributes>
     <attribute name="className" required="true">
       Required, as there is no default
     </attribute>
     <attribute name="optionFlag" required="false">
       If you want the interceptor to trigger on certain message depending on the message's option flag,
       you can setup the interceptors flag here.
       The default value is <code>0</code>, meaning this interceptor will trigger on all messages.
     </attribute>
   </attributes>
  </subsection>

  <subsection name="org.apache.catalina.tribes.group.interceptors.DomainFilterInterceptor Attributes">
   <attributes>
     <attribute name="domain" required="true">
       The logical cluster domain that this Interceptor accepts.
       Two different type of values are possible:<br/>
       1. Regular string values like &quot;staging-domain&quot; or &quot;tomcat-cluster&quot; will be converted into bytes
       using ISO-8859-1 encoding.<br/>
       2. byte array in string form, for example {216,123,12,3}<br/>
     </attribute>
     <attribute name="logInterval" required="false">
       This value indicates the interval for logging for messages from different domains.
       The default is 100, which means that to log  per 100 messages.
     </attribute>
   </attributes>
  </subsection>
  <subsection name="org.apache.catalina.tribes.group.interceptors.FragmentationInterceptor Attributes">
   <attributes>
     <attribute name="expire" required="false">
       How long do we keep the fragments in memory and wait for the rest to arrive.
       The default is 60000 ms.
     </attribute>
     <attribute name="maxSize" required="false">
       The maximum message size in bytes. If the message size exceeds this value, this interceptor fragments the message and sends them.
       If it is less than this value, this interceptor does not fragment the message and sent in as one message. The default is 1024*100.
     </attribute>
   </attributes>
  </subsection>
  <subsection name="org.apache.catalina.tribes.group.interceptors.MessageDispatchInterceptor Attributes">
   <attributes>
     <attribute name="optionFlag" required="false">
       The default and hard coded value is <code>8 (org.apache.catalina.tribes.Channel.SEND_OPTIONS_ASYNCHRONOUS)</code>.
       The dispatcher will trigger on this value only, as it is predefined by Tribes.
     </attribute>
     <attribute name="alwaysSend" required="false">
       What behavior should be executed when the dispatch queue is full. If <code>true</code> (default), then the message is
       is sent synchronously, if <code>false</code> an error is thrown.
     </attribute>
     <attribute name="maxQueueSize" required="false">
       Size in bytes of the dispatch queue, the default value is <code> 1024*1024*64 (64 MiB)</code> sets the maximum queue size for the dispatch queue
       if the queue fills up, one can trigger the behavior, if <code>alwaysSend</code> is set to true, the message will be sent synchronously
       if the flag is false, an error is thrown
     </attribute>
     <attribute name="maxThreads" required="false">
       The maximum number of threads in this pool, default is 10.
     </attribute>
     <attribute name="maxSpareThreads" required="false">
       The number of threads to keep in the pool, default is 2.
     </attribute>
     <attribute name="keepAliveTime" required="false">
       Maximum number of milliseconds of until Idle thread terminates. Default value is 5000(5 seconds).
     </attribute>
   </attributes>
  </subsection>
  <subsection name="org.apache.catalina.tribes.group.interceptors.TcpFailureDetector Attributes">
   <attributes>
     <attribute name="connectTimeout" required="false">
       Specifies the timeout, in milliseconds, to use when attempting a TCP connection
       to the suspect node. Default is 1000.
     </attribute>
     <attribute name="performSendTest" required="false">
       If true is set, send a test message to the suspect node. Default is true.
     </attribute>
     <attribute name="performReadTest" required="false">
       If true is set, read the response of the test message that sent. Default is false.
       <strong>Note:</strong> if <code>performSendTest</code> is false, this attribute will have no effect.
     </attribute>
     <attribute name="readTestTimeout" required="false">
       Specifies the timeout, in milliseconds, to use when performing a read test
       to the suspicious node. Default is 5000.
     </attribute>
     <attribute name="removeSuspectsTimeout" required="false">
       The maximum time(in seconds)  for remove from removeSuspects. Member of
       removeSuspects will be automatically removed after removeSuspectsTimeout.
       If a negative value specified, the removeSuspects members never be
       removed until disappeared really. If the attribute is not provided,
       a default of 300 seconds (5 minutes) is used.
     </attribute>
   </attributes>
  </subsection>
  <subsection name="org.apache.catalina.tribes.group.interceptors.TcpPingInterceptor Attributes">
   <attributes>
     <attribute name="interval" required="false">
       If useThread == true, defines the interval of sending a ping message.
       default is 1000 ms.
     </attribute>
     <attribute name="useThread" required="false">
       Flag of whether to start a thread for sending a ping message.
       If set to true, this interceptor will start a local thread for sending a ping message.
       if set to false, channel heartbeat will send a ping message.
       default is false.
     </attribute>
   </attributes>
  </subsection>
  <subsection name="org.apache.catalina.tribes.group.interceptors.ThroughputInterceptor Attributes">
   <attributes>
     <attribute name="interval" required="false">
       Defines the interval in number of messages when we are to report the throughput statistics.
       The report is logged to the <code>org.apache.juli.logging.LogFactory.getLog(ThroughputInterceptor.class)</code>
       logger under the <code>INFO</code> level.
       Default value is to report every <code>10000</code> messages.
     </attribute>
   </attributes>
  </subsection>
  <subsection name="org.apache.catalina.tribes.group.interceptors.EncryptInterceptor Attributes">
   <p>
     The EncryptInterceptor adds encryption to the channel messages carrying
     session data between nodes.
   </p>
   <p>
     If using the <code>TcpFailureDetector</code>, the <code>EncryptInterceptor</code>
     <i>must</i> be inserted into the interceptor chain <i>before</i> the
     <code>TcpFailureDetector</code>. This is because when validating cluster
     members, <code>TcpFailureDetector</code> writes channel data directly
     to the other members without using the remainder of the interceptor chain,
     but on the receiving side, the message still goes through the chain (in reverse).
     Because of this asymmetry, the <code>EncryptInterceptor</code> must execute
     <i>before</i> the <code>TcpFailureDetector</code> on the sender and <i>after</i>
     it on the receiver, otherwise message corruption will occur.
   </p>
   <p>
     The EncryptInterceptor uses the timestamp of the message to provide replay
     protection. For this to be effective, clock skew between cluster nodes
     should be minimised. If not, it is likely a high proportion of valid
     messages will be rejected.
   </p>
   <attributes>
     <attribute name="encryptionAlgorithm" required="false">
       <p>The encryption algorithm to be used, including the mode and padding.
       Please see
       <a href="https://docs.oracle.com/javase/8/docs/technotes/guides/security/StandardNames.html">https://docs.oracle.com/javase/8/docs/technotes/guides/security/StandardNames.html</a>
       for the standard JCA names that can be used. Algorithms from other JCA
       providers are also supported.</p>

       <p>The EncryptInterceptor currently supports the following standard
       <a href="https://en.wikipedia.org/wiki/Block_cipher_mode_of_operation">block-cipher modes</a>:
       CBC, CFB, OFB and GCM. Of these, it is recommended that GCM is always
       used.</p>

       <p>The length of the key will specify the flavor of the encryption
       algorithm to be used, if applicable (e.g. AES-128 versus AES-256).</p>

       <p>The default algorithm is <code>AES/CBC/PKCS5Padding</code> for
       backwards compatability but it is recommended that
       <code>AES/GCM/NoPadding</code> is used.</p>
     </attribute>
     <attribute name="encryptionKey" required="true">
       <p>The key to be used with the encryption algorithm.</p>

       <p>The key should be specified as hex-encoded bytes of the appropriate
       length for the algorithm (e.g. 16 bytes / 32 characters / 128 bits for
       AES-128, 32 bytes / 64 characters / 256 bits for AES-256, etc.).</p>
     </attribute>
     <attribute name="replayWindowTime" required="false">
       <p>Messages with a timestamp before the current time less this window or
       after the current time plus this window will be rejected. This window
       needs to account for clock skew across the cluster as well as the
       expected maximum delay between messages being sent and received.
       Specified in milliseconds. If not specified, the default value of 10000
       (10 seconds) will be used.</p>
     </attribute>
     <attribute name="replayWindowMessageCount" required="false">
       <p>The number of past messages for which the nonces will be tracked to
       prevent replay attacks. Messages with a nonce that has already been
       tracked will be rejected. If not specified, the default value of 8192
       will be used.</p>

       <p>If messages are received at a high rate, it is possible that a nonce
       will be removed from the list of tracked nonces before
       <code>replayWindowTime</code> milliseconds have elapsed. If that happens,
       any message with a timestamp older than the last nonce evicted from the
       list of tracked nonces will also be rejected.</p>
     </attribute>
   </attributes>
  </subsection>
</section>

<section name="Nested Components">

  <subsection name="StaticMember Attributes">
    <p><b>LocalMember:</b> <br/>
    Static member that is the local member of the static cluster group.
    </p>
    <attributes>
      <attribute name="className" required="true">
        Only one implementation available:<code>org.apache.catalina.tribes.membership.StaticMember</code>
      </attribute>
      <attribute name="port" required="false">
        There is no need to set.
        The value of this attribute inherits from the cluster receiver setting.
      </attribute>
      <attribute name="securePort" required="false">
        There is no need to set.
        The value of this attribute inherits from the cluster receiver setting.
      </attribute>
      <attribute name="host" required="false">
        There is no need to set.
        The value of this attribute inherits from the cluster receiver setting.
      </attribute>
      <attribute name="domain" required="false">
        The logical cluster domain for that this static member listens for cluster messages.
        Two different type of values are possible:<br/>
        1. Regular string values like &quot;staging-domain&quot; or &quot;tomcat-cluster&quot; will be converted into bytes
        using ISO-8859-1 encoding.
        2. byte array in string form, for example {216,123,12,3}<br/>
      </attribute>
      <attribute name="uniqueId" required="true">
        A universally uniqueId for this static member.
        The values must be 16 bytes in the following form:<br/>
        1. byte array in string form, for example {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}<br/>
      </attribute>
    </attributes>

    <p><b>Member:</b> <br/>
    Static member that add to the static cluster group.
    </p>
    <attributes>
      <attribute name="className" required="true">
        Only one implementation available:<code>org.apache.catalina.tribes.membership.StaticMember</code>
      </attribute>
      <attribute name="port" required="true">
        The port that this static member listens to for cluster messages
      </attribute>
      <attribute name="securePort" required="false">
        The secure port this static member listens to for encrypted cluster messages
        default value is <code>-1</code>, this value means the member is not listening on a secure port
      </attribute>
      <attribute name="host" required="true">
        The host (or network interface) that this static member listens for cluster messages.
        Three different type of values are possible:<br/>
        1. IP address in the form of &quot;216.123.1.23&quot;<br/>
        2. Hostnames like &quot;tomcat01.mydomain.com&quot; or &quot;tomcat01&quot; as long as they resolve correctly<br/>
        3. byte array in string form, for example {216,123,12,3}<br/>
      </attribute>
      <attribute name="domain" required="false">
        The logical cluster domain for that this static member listens for cluster messages.
        Two different type of values are possible:<br/>
        1. Regular string values like &quot;staging-domain&quot; or &quot;tomcat-cluster&quot; will be converted into bytes
        using ISO-8859-1 encoding.<br/>
        2. byte array in string form, for example {216,123,12,3}<br/>
      </attribute>
      <attribute name="uniqueId" required="true">
        A universally uniqueId for this static member.
        The values must be 16 bytes in the following form:<br/>
        1. byte array in string form, for example {0,1,2,3,4,5,6,7,8,9,10,11,12,13,14,15}<br/>
      </attribute>
    </attributes>
  </subsection>
  <!--TODO Document all the interceptors-->

</section>


</body>

</document>
